necessary for such photography. However^ with the naked eye (or proper 

 photography) one can gain considerable insight into the three dimensionality 

 encountered in the wake of these "two-dimensional" bodies. The literature 

 verifies that such flows can be extremely predominant (Reference lO) in 

 reality , 



When experimental investigations are considered in water^ it is 

 apparent that with discrete sizing of characteristic body lengths of models^ 

 it is important that the water velocities needed to meet specific parameter 

 values are adaptable to the necessary bubble quality. Although it has been 

 definitely verified that velocities can exceed certain values without wire 

 breakage, there is a decrease in bubble quality with increased water velo- 

 city, not to mention the increased likelihood of vortex shedding error which 

 undoubtedly occurs at higher flow velocities. 



Further flexibility in the bubble technique is attained by allowing 

 a particular portion of a metallic model to act as a cathode terminal (see 

 Reference 2), When this was attempted, the bubbles were unevenly dragged 

 from the body, apparently because of excessive boundary- layer thickness. 

 Therefore, when ■ the model itself is used as a cathode terminal, the local 

 fluid velocity has to be sufficient to drag the bubbles into the flow. A 

 dielectric covering (paint or plastic tape) can easily be applied to the 

 entire surface of the body in the flow with the exception of the region 

 where the bubbles are to be produced. Another way to achieve the same 

 effect is to imbed a platinum wire or other conductor into the surface of 

 a plastic or nonconducting body. One has then only to energize either the 

 entire body or the imbedded conductor with a dc voltage to obtain a steady 

 streeim of bubbles from any point on the surface of the body. Pulsed 

 excitation was found rather -unsuccessful due to the uneven shedding of 

 bubbles between electric pulses . An attempt was made to utilize the trail- 

 ing edge of the foil shapes in such a manner, but the velocities in this 

 region for very small angles of attack were apparently insufficient to 

 drag bubbles into the flow evenly all along the entire span of the body. 

 Although the bubbles were not dragged evenly (as a sheet of bubbles) into 

 the flow along the span length, one could observe whether or not the 



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